1. Field
The invention relates generally to the field of telecommunications, and more particularly to mechanisms for reducing search time in a wireless network based on power spectral density.
2. Background
Wireless communication systems are widely deployed to provide various types of communication content such as voice, data, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources (e.g., bandwidth and transmit power). Examples of such multiple-access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, 3GPP Long Term Evolution (LTE) systems, Ultra Mobile Broadband (UMB) systems, and orthogonal frequency division multiple access (OFDMA) systems.
Generally, a wireless multiple-access communication system can simultaneously support communication for multiple wireless terminals. Each terminal communicates with one or more base stations via transmissions on the forward and reverse links. The forward link (or downlink) refers to the communication link from the base stations to the terminals, and the reverse link (or uplink) refers to the communication link from the terminals to the base stations. This communication link may be established via a single-in-single-out, multiple-in-signal-out or a multiple-in-multiple-out (MIMO) system.
A MIMO system employs multiple (NT) transmit antennas and multiple (NR) receive antennas for data transmission. A MIMO channel formed by the NT transmit and NR receive antennas may be decomposed into NS independent channels, which are also referred to as spatial channels, where NS≦min{NT, NR}. Each of the NS independent channels corresponds to a dimension. The MIMO system can provide improved performance (e.g., higher throughput and/or greater reliability) if the additional dimensionalities created by the multiple transmit and receive antennas are utilized.
A MIMO system supports a time division duplex (TDD) and frequency division duplex (FDD) systems. In a TDD system, the forward and reverse link transmissions are on the same frequency region so that the reciprocity principle allows the estimation of the forward link channel from the reverse link channel. This enables the access point to extract transmit beamforming gain on the forward link when multiple antennas are available at the access point.
At power up or upon system loss, if the user equipment (UE) cannot acquire a system using the stored channels list (list of channels on which UE has previously camped) then the UE may do a frequency scan. The frequency scan involves a code space search on all frequencies in a given band that have receive power above the receiver noise floor. It may take a relatively long time (2-3 minutes) to complete in a polluted radio frequency environments. Additionally, power consumption for the UE is high in completing the frequency scan. Therefore, the time necessary to acquire a system is heavily dependent on the number of frequencies that must be searched. By reducing the frequency space (that is, the frequencies which must be scanned) without compromising the probability of detection, a UE can expedite system acquisition and reduce power consumption during an out of service search (OOS).
There is therefore a need in the art for reducing the frequency space without compromising the probability of detection.